1. Technical Field
The invention relates in general to a transmitter and a frequency deviation reduction method thereof.
2. Background
Referring to FIG. 1, a schematic illustration of a conventional polar transmitter is shown. The conventional polar transmitter 100 includes a polar signal generating and processing circuit 110, an amplitude modulation (AM) unit 120, an all digital phase-locked loop (ADPLL) 130 and a combining unit 140. The polar signal generating and processing circuit 110 generates an amplitude component α and a phase component θ, and processes the phase component θ to obtain a frequency component f. The AM unit 120 performs amplitude modulation on the amplitude component α to obtain an adjusted amplitude component A. The ADPLL 130 includes a frequency modulation (FM) unit 132 and a digital controlled oscillator (DCO) 134. The FM unit 132 and the DCO 134 process the frequency component f to obtain an adjusted frequency component F. The combining unit 140 combines the adjusted amplitude component A and the adjusted frequency component F to generate a transmitted signal RF. To the polar transmitter 100 with wide bandwidth, a peak frequency easily occurs in the frequency component f. In other words, the higher the frequency of the frequency component f, the more complexity of the design of the DCO 134. Besides, DCO 134 with large frequency deviations also suffers nonlinearity problems, thereby degrading the overall performance of the polar transmitter 100.